1. Technical Field
Example embodiments relate to a method of arranging fuses in a fuse box of a semiconductor memory device and a semiconductor memory device including such an arrangement.
2. Description of the Related Art
A semiconductor memory device may not function properly because one of its memory cells has a defect. Consequently, an entire memory device may be discarded merely because of a defect in one or a small number of its memory cells, thus decreasing manufacturing yield. However, a defective memory device may be salvaged by replacing the defective cell with a redundancy cell in the memory device. A repair operation may be performed by positioning a spare row array and a spare column array in each sub-array block of the semiconductor memory device and replacing the defective memory cell with a spare redundancy cell. Thus, the repair operation may be performed by selecting a defective memory cell and changing the relevant address of the defective memory cell to the address signal of a redundancy cell with a programming operation. The programming operation may include an electric fusing method of melting and cutting fuses using over current, a method of burning and cutting fuses using a laser beam, and a method of shorting a junction using a laser beam.
FIG. 1 is a block diagram of a conventional semiconductor memory device 100. Referring to FIG. 1, the conventional semiconductor memory device 100 may include a memory cell array 110 and two sets 150 and 160 of fuse boxes (FBs). The memory cell array 110 may include a plurality of sub-array blocks (SABs), and each SAB may include normal cells and redundancy cells. Each FB may include a plurality of fuses. When a defect occurs in a cell in one of the SABs, the appropriate fuse may be fused, and the row address/column address of the defective cell may be replaced with the row address/column address of a redundancy cell, thus replacing the defective cell with the redundancy cell.
FIG. 2 illustrates the structure of the fuse box (FB) of FIG. 1. Referring to FIG. 2, the FB may include a plurality of fuses 210, 220, 230, 240, 250, and 260. The interval between two adjacent fuses may be called a pitch. When the pitch is relatively small, two or more fuses may be inadvertently included in the spot 290 of a laser beam during the cutting of the appropriate fuse. Because the spot 290 of the laser beam may inadvertently cut one or more adjacent fuses during the process of cutting the appropriate fuse, proper performance of the repair operation may be hindered. Accordingly, it may be necessary to use laser equipment having a relatively small spot size, which may be relatively expensive, to accommodate the relatively small pitch size of conventional scaled-down semiconductor memory devices. Alternatively, the pitch size may be increased such that only one fuse is included in the spot 290 of a laser beam generated by conventional laser beam equipment. However, increasing pitch size will consequently increase the size of the memory device.